1. Field of the Invention
The invention relates to an apparatus for the detection of contaminants in an elongated textile product, such as a yarn or a thread.
Before spinning, raw fibers, e.g. cotton fibers, are mechanically cleaned in carding machines, where many contaminants, such as fragments of cotton shells, can be removed. Still, it cannot be ruled out that smaller contaminants, e.g. foreign fibers, remain in the yarn. Therefore, additional cleaning is required for obtaining a yarn of high quality.
2. Description of the Prior Art
Several devices are known for detecting and removing yarn faults, such as too thick or too thin sections of yarn. These so-called yarn cleaners automatically cut away the respective sections of the yarn.
In recent time yarn manufacturers have been endeavoring to detect and control not only such thickness variations, but also contaminants in the yarn, especially those due to foreign fiber material.
Such a device is e.g. known from the European patent EP-0 197 763. Its principle of measurement is based on diffusely illuminating the yarn through opaque zones of material such that the yarn does not differ in brightness from its background and therefore becomes invisible for a light detector as long as it does not contain a contaminant. In this way the influence of the yarn thickness on the detector signal can be eliminated.
The solution described in the above patent has the disadvantage that the yarn cannot be inserted into the apparatus in a conventional way as it is done in known yarn cleaners. This is due to the fact that the yarn runs at the bottom of a channel with angular walls to prevent the entry of foreign light.
Such an apparatus can therefore not be used in combination with conventional yarn insertion devices.